2. Field of the Invention
The present invention relates, in general, to multi-component electronic circuits, and more specifically, to an assembly and method for assembling an integrated circuit that is tightly coupled to inductor and capacitor elements on a single leadframe.
3. Relevant Background
Many passive components (e.g., capacitors, inductors and resistors) cannot be cost effectively integrated onto a monolithic integrated circuit because of their size. Also, the limitations in a particular integrated circuit processing technology may prohibit inductors or high valued capacitors and resistors. Typically, large valued inductors and capacitors are manufactured as separate components and interconnected with the integrated circuit to provide the desired functionality.
For example, in power supplies such as AC-DC and DC-DC converters, large value inductors and capacitors are required that cannot be provided on the integrated circuit. Most such circuits are manufactured using multiple components interconnected by printed wiring on a circuit board. However, there is increasing demand for single device solutions for power supply circuits to reduce overall system size.
It is desirable from a manufacturer's and user's standpoint that packaged circuits require as few external components as possible. This eases assembly and lowers costs for the end user while increasing value added to the manufacturer. Hence, integrated circuit manufacturers are increasingly offering multi-component modules that include one or more integrated circuit chips packaged together with external passive components such as inductive and capacitor elements.
Another advantage of multi-component packaging is that stray and parasitic capacitance and inductance associated with leads and circuit board traces can be eliminated. However, stray capacitance and inductance associated with wire bonds connecting multiple chips remain a problem. In conventional multi-component modules, components are mounted on a substrate or leadframe in the same plane and coupled together by wire bonds. This "planar" arrangement results in large packages making the packages more difficult to use, expensive to manufacture and costly in terms of circuit board real estate for the user.
Some attempts have been made to vertically stack integrated circuits with associated passive components. Some of these efforts require three dimensionally formed lead frames that are difficult to manufacture and difficult to work with on an assembly line. Also, the integrated circuits could be left exposed on the surfaces of the vertical stack. Moreover, existing vertically stacked assemblies require relatively difficult assembly adding to the production cost of the component. It is desirable to use planar lead frames and to avoid exposure of the integrated circuit chip.